1. Field of the Invention
The present invention relates to a wireless communication system having a hierarchical cell structure. More particularly, the present invention relates to a method and an apparatus for X2 interwork between eNBs using a gateway.
2. Description of the Related Art
A Long Term Evolution (LTE) system provides an S1 handover using an S1 interface between a Mobility Management Entity/Serving-GateWay (MME/S-GW) and an eNB and an X2 handover using an X2 interface between eNBs. However, since the S1 handover is performed via an MME/S-G, it may generate an overhead to a core network and a handover delay time increases, so that the X2 handover between eNBs is preferred.
Meanwhile, recently, for swift communication of user equipment (UE), a wireless communication system provides a wireless communication system of a hierarchical cell structure where eNBs having different cell coverages co-exist. For example, a wireless communication system provides a communication system where a small cell like a pico cell and a macro cell co-exist. Particularly, the current LTE-A standard discusses an alternative for improving an entire system performance using a small eNB.
FIG. 1 illustrates a general LTE system configuration.
Referring to FIG. 1, the LTE system includes macro base stations (eNBs) 100-1 to 100-3, small base stations (pico eNBs or home eNBs) 110-1 to 110-4, an MME/S-GWs 120-1 and 120-2 which are core networks, and a small gateway (pico GW or home GW) 130. Here, the macro eNBs 100-1 to 100-3 interwork using the MME/S-GWs 120-1 and 120-2 and an S1 interface, and the home eNBs 110-1 to 110-4 operate by interworking using the pico GW 130 and an S1 interface in order to minimize an influence of the core network. Particularly, referring to the LTE system standard, the macro eNBs 100-1 to 100-3 and home eNBs 110-1 to 110-4 are defined to operate by connecting with an X2 interface via the small GW 130.
However, since the standard does not describe a specific alternative for connecting with the X2 interface via the small GW, a specific alternative needs to be proposed.